This invention relates to methods of forming refractory metal nitride layers (including silicon nitride layers) on substrates using a vapor deposition process with a refractory metal halide (preferably, fluoride) precursor compound, a disilazane, and optionally a silicon precursor compound. The formed refractory metal (silicon) nitride layers are particularly useful as diffusion barriers for polysilicon substrates to reduce diffusion of oxygen, copper, or silicon.
In integrated circuit manufacturing, microelectronic devices such as capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and ferroelectric memory (FERAM) devices. Capacitors typically consist of two conductors acting as electrodes, such as parallel metal (e.g., platinum) or polysilicon plates, that are insulated from each other by a layer of dielectric material.
Historically, silicon dioxide has generally been the dielectric material of choice for capacitors. However, the continuous shrinkage of microelectronic devices over the years has led to dielectric layers approaching only 10 xc3x85 in thickness (corresponding to 4 or 5 molecules). To reduce current tunneling through thin dielectric layers, high dielectric metal-containing layers, such as Al2O3, TiO2, ZrO2 HfO2, Ta2O5, (Ba,Sr)TiO3. Pb(Zr,Ti)O3 and SrBi2Ti2O9, have been developed to replace SiO2 layers. However, these metal-containing layers can provide high leakage paths and channels for oxygen diffusion, especially during annealing. Also, an undesirable interfacial layer of SiO2 is frequently created by oxidation of polysilicon during the annealing of the dielectric layer.
One way to address these problems is to deposit a thin, conductive, amorphous, metal nitride barrier layer on the substrate prior to the deposition of the thin resistive metal oxide layer. For example, reactive metal silicon nitride barrier metal layers are used to protect polysilicon from oxygen diffusion prior to applying very thin (i.e., less than 10 xc3x85) barium strontium titanate dielectric films.
Refractory metal nitrides and refractory metal silicon nitrides, such as titanium nitride (Tixe2x80x94N), tantalum nitride (Taxe2x80x94N), tungsten nitride (Wxe2x80x94N), molybdenum nitride (Moxe2x80x94N), titanium silicon nitride (Tixe2x80x94Sixe2x80x94N), tantalum silicon nitride (Taxe2x80x94Sixe2x80x94N) and tungsten silicon nitride (Wxe2x80x94Sixe2x80x94N), are also useful as conductive barrier layers between silicon substrates and copper interconnects to reduce copper diffusion. This copper diffusion has led to degradation of device reliability, causing semiconductor manufacturers to turn toward other less conductive metals, such as aluminum and tungsten.
Further improvements in high temperature adhesion and diffusion resistance can be realized when about 4 to about 30 atom % silicon is incorporated to form a more amorphous metal silicon nitride layer. Examples of refractory metal silicon nitrides that are useful as barrier layers include tantalum silicon nitride (Taxe2x80x94Sixe2x80x94N), titanium silicon nitride (Tixe2x80x94Sixe2x80x94N), and tungsten silicon nitride (Wxe2x80x94Sixe2x80x94N).
Methods for using physical vapor deposition (PVD) methods, such as reactive sputtering, to form Taxe2x80x94Sixe2x80x94N barrier layers are known. Hara et al., xe2x80x9cBarrier Properties for Oxygen Diffusion in a TaSiN Layer,xe2x80x9d Jpn J. Appl.-Phys., 36(7B), L893 (1997) describe noncrystalline, low resistivity Taxe2x80x94Sixe2x80x94N layers that acts as a barrier to oxygen diffusion during high temperature annealing at 650xc2x0 C. in the presence Of O2. The Taxe2x80x94Sixe2x80x94N layers are formed by using radio-frequency reactive sputtering with pure Ta and Si targets on a 100 nm thick polysilicon layer. Layers having relatively low silicon content, such as Ta50Si16N34. are stated to have a desirable combination of good diffusion barrier resistance along with low sheet resistance. These Taxe2x80x94Sixe2x80x94N barrier layers have improved peel resistance over Taxe2x80x94N barrier layers during annealing conditions.
Lee et al., xe2x80x9cStructural and chemical stability of Taxe2x80x94Sixe2x80x94N thin film between Si and Cu,xe2x80x9d Thin Solid Films, 320 :141-146 (1998) describe amorphous, ultra-thin (i.e., less than 100 xc3x85) tantalum-silicon-nitrogen barrier films between silicon and copper interconnection materials used in integrated circuits. These barrier films suppress the diffusion of copper into silicon, thus improving device reliability. Barrier films having compositions ranging from Ta43Si04N53 to Ta60Si11N29 were deposited on silicon by reactive sputtering from Ta and Si targets in an Ar/N2 discharge, followed by sputter-depositing copper films.
However, when PVD methods are used, the stoichiometric composition of the formed metal nitride and metal silicon nitride barrier layers such as Taxe2x80x94N and Taxe2x80x94Sixe2x80x94N can be non-uniform across the substrate surface due to different sputter yields of Ta, Si, and N. Due to the resulting poor layer conformality, defects such as pinholes often occur in such layers creating pathways to diffusion. As a result, the effectiveness of a physically deposited diffusion barrier layer is dependent on the layer being sufficiently thick.
Vapor deposition processes such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes are preferable to PVD processes in order to achieve the most efficient and uniform barrier layer coverage of substrate surfaces. There remains a need for a vapor deposition process to form refractory metal nitrides and refractory metal silicon nitride barrier layers (especially Taxe2x80x94N and Taxe2x80x94Sixe2x80x94N layers) on substrates, such as semiconductor substrates or substrate assemblies.
This invention is directed to methods of using vapor deposition processes to deposit refractory metal (silicon) nitride layers (i.e., refractory metal nitride and refractory metal silicon nitride layers) on substrates. The process involves combining one or more refractory metal halide precursor compounds, one or more nitrogen precursor compounds (disilazanes), and optionally one or more silicon precursor compounds.
In one embodiment, the present invention provides a method of forming a layer on a substrate (preferably, in a process of manufacturing a semiconductor structure). The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer); providing a vapor that includes one or more refractory metal precursor compounds of the formula MYn (Formula I), wherein M is a refractory metal (e.g., Ti, Nb, Ta, Mo, and W), each Y is independently a halogen atom (preferably, F, Cl, I, or combinations thereof, and more preferably, F), and n is an integer selected to match the valence of the metal M (e.g., n=5 when M=Ta); providing a vapor that includes one or more disilazanes of the formula (R)xH3-xSiNHSi(R)xH3-x, wherein each R is independently an organic group, and x is 1 to 3; and directing the vapors that include the one or more refractory metal precursor compounds and the one or more disilazanes to the substrate to form a refractory metal nitride layer (e.g., tantalum nitride) on one or more surfaces of the substrate. The resultant nitride layer (or silicon nitride layer) is typically suitable for use as a diffusion barrier layer, which is particularly advantageous when the substrate includes a silicon-containing surface.
The present invention also provides a method of manufacturing a memory device. The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly) that includes a silicon-containing surface; providing a vapor that includes one or more refractory metal precursor compounds of the formula MYn (Formula I), wherein M is a refractory metal, each Y is independently a halogen atom, and n is an integer selected to match the valence of the metal M; directing the vapor that includes the one or more precursor compounds of the Formula I to the substrate and allowing the one or more compounds to chemisorb on the silicon-containing surface; providing a vapor that includes one or more disilazanes of the formula (R)xH3-xSiNHSi(R)xH3-x, wherein each R is independently an organic group, and x is 1 to 3; directing the vapor that includes the one or more disilazanes to the substrate with the chemisorbed compounds thereon to form a refractory metal nitride barrier layer on the silicon-containing surface; providing a first electrode on the barrier layer; providing a high dielectric material over at least a portion of the first electrode; and providing a second electrode over the high dielectric material.
Preferred methods of the present invention also include steps of providing a vapor that includes one or more silicon precursor compounds and directing the vapor to the substrate to form a refractory metal silicon nitride layer. Optionally, the methods can also provide one or more reaction gases other than the disilazanes and silicon precursor compounds and direct the one or more reaction gases to the substrate. Also, in certain embodiments, the methods can provide a vapor that includes one or more metal-containing precursor compounds of a formula different from Formula I and direct this vapor to the substrate.
The present invention also provides a vapor deposition apparatus that includes: a vapor deposition chamber having a substrate positioned therein; and one or more vessels that include one or more refractory metal precursor compounds of the formula MYn (Formula 1), wherein M is a refractory metal, each Y is independently a halogen atom, and n is an integer selected to match the valence of the metal M; and one or more vessels that include one or more disilazanes of the formula (R)xH3-xSiNHSi(R)xH3-x, wherein each R is independently an organic group, and x is 1 to 3. Optionally, the apparatus can include one or more vessels with one or more silicon precursor compounds therein and/or one or more reaction gases other than the disilazanes and silicon precursor compounds therein.
The methods of the present invention can utilize a chemical vapor deposition (CVD) process, which can be pulsed, or an atomic layer deposition (ALD) process (a self-limiting vapor deposition process that includes a plurality of deposition cycles, typically with purging between the cycles). Preferably, the methods of the present invention use ALD. In one embodiment of an ALD process, the refractory metal nitride layer is formed by alternately introducing the one or more vaporized precursor compounds and one or more vaporized disilazanes into a deposition chamber during each deposition cycle.
xe2x80x9cSubstratexe2x80x9d as used herein refers to any base material or construction upon which a metal-containing layer can be deposited. The term xe2x80x9csubstratexe2x80x9d is meant to include semiconductor substrates and also include non-semiconductor substrates such as films, molded articles, fibers, wires, glass, ceramics, machined metal parts, etc.
xe2x80x9cSemiconductor substratexe2x80x9d or xe2x80x9csubstrate assemblyxe2x80x9d as used herein refers to a semiconductor substrate such as a metal electrode, base semiconductor layer or a semiconductor substrate having one or more layers, structures, or regions formed thereon. A base semiconductor layer is typically the lowest layer of silicon material on a wafer or a silicon layer deposited on another material, such as silicon on sapphire. When reference is made to a substrate assembly, various process steps may have been previously used to form or define regions, junctions, various structures or features, and openings such as capacitor plates or barriers for capacitors.
xe2x80x9cLayerxe2x80x9d as used herein refers to any metal-containing layer that can be formed on a substrate from the precursor compounds of this invention using a vapor deposition process. The term xe2x80x9clayerxe2x80x9d is meant to include layers specific to the semiconductor industry, such as xe2x80x9cbarrier layer,xe2x80x9d xe2x80x9cdielectric layer,xe2x80x9d and xe2x80x9cconductive layer.xe2x80x9d (The term xe2x80x9clayerxe2x80x9d is synonymous with the term xe2x80x9cfilmxe2x80x9d frequently used in the semiconductor industry.) The term xe2x80x9clayerxe2x80x9d is also meant to include layers found in technology outside of semiconductor technology, such as coatings on glass.
xe2x80x9cBarrier layerxe2x80x9d as used herein refers to a conductive, interfacial layer that can reduce diffusion of ambient oxygen through a dielectric layer into a semiconductor substrate (typically a polysilicon substrate) or can reduce diffusion of one layer into another, such as a copper conductive layer into a semiconductor substrate (typically a polysilicon substrate). For this invention, the barrier layer is a tantalum nitride or tantalum silicon nitride layer.
xe2x80x9cRefractory metalxe2x80x9d as defined by Webster""s New Universal Unabridged Dictionary (1992) is a metal that is difficult to fuse, reduce, or work. For the purposes of this invention, the term xe2x80x9crefractory metalxe2x80x9d is meant to include the Group IVB metals (i.e., titanium (Ti), zirconium (Zr), hafnium (Hf)); the Group VB metals (i.e., vanadium (V), niobium (Nb), tantalum (Ta)); and the Group VIB metals (i.e., chromium (Cr), molybdenum (Mo) and tungsten (W)).
xe2x80x9cPrecursor compoundxe2x80x9d as used herein refers to refractory metal precursor compounds, nitrogen precursor compounds, silicon precursor compounds, and other metal-containing precursor compounds, for example. A suitable precursor compound is one that is capable of forming, either alone or with other precursor compounds, a refractory metal-containing layer on a substrate using a vapor deposition process. The resulting refractory metal-containing layers also typically include nitrogen and optionally silicon. Such layers are often useful as diffusion barrier layers (i.e., barrier layers).
xe2x80x9cDeposition processxe2x80x9d and xe2x80x9cvapor deposition processxe2x80x9d as used herein refer to a process in which a metal-containing layer is formed on one or more surfaces of a substrate (e.g., a doped polysilicon wafer) from vaporized precursor compound(s). Specifically, one or more metal precursor compounds are vaporized and directed to one or more surfaces of a heated substrate (e.g., semiconductor substrate or substrate assembly) placed in a deposition chamber. These precursor compounds form (e.g., by reacting or decomposing) a non-volatile, thin, uniform, metal-containing layer on the surface(s) of the substrate. For the purposes of this invention, the term xe2x80x9cvapor deposition processxe2x80x9d is meant to include both chemical vapor deposition processes (including pulsed chemical vapor deposition processes) and atomic layer deposition processes.
xe2x80x9cChemical vapor depositionxe2x80x9d (CVD) as used herein refers to a vapor deposition process wherein the desired layer is deposited on the substrate from vaporized metal precursor compounds and any reaction gases used within a deposition chamber with no effort made to separate the reaction components. In contrast to a xe2x80x9csimplexe2x80x9d CVD process that involves the substantial simultaneous use of the precursor compounds and any reaction gases, xe2x80x9cpulsedxe2x80x9d CVD alternately pulses these materials into the deposition chamber, but does not rigorously avoid intermixing of the precursor and reaction gas streams, as is typically done in atomic layer deposition or ALD (discussed in greater detail below).
xe2x80x9cAtomic layer depositionxe2x80x9d (ALD) as used herein refers to a vapor deposition process in which numerous consecutive deposition cycles are conducted in a deposition chamber. Typically, during each cycle the metal precursor is chemisorbed to the substrate surface; excess precursor is purged out; a subsequent precursor and/or reaction gas is introduced to react with the chemisorbed layer; and excess reaction gas (if used) and by-products are removed. As compared to the one cycle chemical vapor deposition (CVD) process, the longer duration multi-cycle ALD process allows for improved control of layer thickness by self-limiting layer growth and minimizing detrimental gas phase reactions by separation of the reaction components. The term xe2x80x9catomic layer depositionxe2x80x9d as used herein is also meant to include the related terms xe2x80x9catomic layer epitaxyxe2x80x9d (ALE) (see U.S. Pat. No. 5,256,244 (Ackerman)), molecular beam epitaxy (MBE), gas source MBE, organometallic MBE, and chemical beam epitaxy when performed with alternating pulses of precursor compound(s), reaction gas and purge (i.e., inert carrier) gas.
xe2x80x9cChemisorptionxe2x80x9d as used herein refers to the chemical adsorption of vaporized reactive precursor compounds on the surface of a substrate. The adsorbed species are irreversibly bound to the substrate surface as a result of relatively strong binding forces characterized by high adsorption energies ( greater than 30 kcal/mol), comparable in strength to ordinary chemical bonds. The chemisorbed species are limited to the formation of a monolayer on the substrate surface. (See xe2x80x9cThe Condensed Chemical Dictionaryxe2x80x9d, 10th edition, revised by G. G. Hawley, published by Van Nostrand Reinhold Co., New York, 225 (1981)). The technique of ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. In ALD one or more appropriate reactive precursor compounds are alternately introduced (e.g., pulsed) into a deposition chamber and chemisorbed onto the surfaces of a substrate. Each sequential introduction of a reactive precursor compound is typically separated by an inert carrier gas purge. Each precursor compound co-reaction adds a new atomic layer to previously deposited layers to form a cumulative solid layer. The cycle is repeated, typically for several hundred times, to gradually form the desired layer thickness. It should be understood, however, that ALD can use one precursor compound and one reaction gas.